Air traffic control systems track positions and velocity of aircraft and help prevent aircraft collisions within the vicinity of airports. Air traffic control has traditionally been based on radar surveillance, supplemented more recently with cooperative radio surveillance techniques. Major portions of many aircraft flights take place in relatively remote areas and outside of radio surveillance or radar airspace, and follow procedural separation standards. Procedural separation in oceanic or other remote airspace not covered by ground-based radio surveillance means require the separation of air traffic at significantly larger distances than that used in radio surveillance or radar airspace.